Drinking water is typically extracted from an aquifer and processed in a water treatment system to remove undesired contaminants and impurities, and add a sanitizer, such as chlorine, for example. Water taken from an aquifer may contain a high hydrogen sulfide content, because of surrounding geological features and/or the action of certain bacteria. Unfortunately, hydrogen sulfide gas has an unpleasant odor and it is undesirable to discharge into the atmosphere that can then annoy residents of surrounding neighborhoods, for example.
Some water treatment plants remove or scrub hydrogen sulfide from the water with a caustic scrubbing solution, such as including potassium hydroxide or sodium hydroxide. In such a system, water pumped from the aquifer is first passed through an aerator for extracting a hydrogen sulfide-containing gas flow from the water. The hydrogen sulfide-containing gas flow is then passed through a hydrogen sulfide scrubber including at least one scrubber tank through which the caustic scrubbing solution is circulated and constantly replenished.
A common configuration of a hydrogen sulfide scrubber includes two scrubber tanks each having generally lightweight scrubber media therein. The scrubber tanks may be as offered by the Duall Division of Met-Pro Corporation of Owosso, Mich. under the model series designation PT-500. The scrubber media may be in the form of hollow spheres with passageways therein to provide a large surface area to enhance the capture of hydrogen sulfide from the gas flow and into the scrubbing solution. The hydrogen sulfide scrubber may also include first and second scrubbing solution circulators, each dispensing a scrubbing solution into contact with the scrubber media, a sump for collecting the scrubbing solution, and a circulating pump for circulating the scrubbing solution from the sump and back to the dispenser. The scrubbing solution includes caustic to adjust the pH to a desired level at which the hydrogen sulfide will more readily dissolve into the scrubbing solution.
The caustic material, however, causes a build-up in the scrubber tank, and especially on the scrubber media. This build-up covers and may block the passageways in the scrubber media and reduce the available surface area for extracting the hydrogen sulfide. The build-up also increases the weight of the scrubber media and reduces movement during scrubbing. Moreover, the increased weight may also stress the supporting structure of the tank.
Periodic cleaning is recommended for caustic-based hydrogen sulfide scrubbers. Such cleaning is generally performed by acid washing and is relatively difficult. Accordingly, maintenance may be postponed until the removal of hydrogen sulfide is no longer acceptable. At this point, very costly replacement of the scrubber media may be needed. The use of caustic further requires careful handling, and is relatively expensive when the cost of removing the build-up is considered. The use of caustic also requires a considerable flow of make-up water and a corresponding relatively large discharge of spent scrubber solution into the sewer system.
A significant advance in the area of hydrogen sulfide removal, while reducing build-up in the scrubber, is the use of triazine compound in the scrubber solution as disclosed in published U.S. patent application Ser. No. 2004/0055463 assigned to the present assignee. Despite the improvement offered by the use of the triazine compound versus traditional caustic scrubbing solutions, other odor causing compounds may still be released, such as volatile mercaptans. The mercaptans may cause an undesirable odor in the vicinity of the scrubber. Of course, there is also a continuing desire to increase hydrogen sulfide removal and reduce build-up on the scrubbing media.